1. Field of the Invention
The invention relates to a method and a device for the continuous transmission of a video from a server to a number of client machines over a communication network.
2. Related Art in the Invention
It is known to transmit videos over a communication network, such as the Internet for example.
However, the implementation of such a transmission remains difficult since this type of network has been designed more for the transmission of files than for the transmission of continuous data at a high rate.
The difficulty increases when it is a question of transmitting a video from a server to a number of client machines, the characteristics of which are heterogeneous.
This is because in this case it is necessary to satisfy a number of users of client machines that are connected to the server and have different bandwidths and thus individual computing and display capabilities.
A system for the transmission of videos over a communication network is known from the article entitled “Adaptive Video Distribution Model of QHD (Quadruple HD) with JPEG2000”.
In the said system, a server transmits a video in the Motion JPEG2000 format to a number of users who each receive the same amount of data and who may locally manipulate the data that constitute the said video, depending on their own requirements.
However, this method is not satisfactory in that the transmission of a single version of the video at a fixed rate will not satisfy all users.
This is because some users will receive too high a rate, thus causing a loss of data, while others will not receive enough data in relation to their available bandwidth.
Another transmission system is known from the article entitled “TCP-compatible rate control for FGS layered multicast video transmission based on a clustering algorithm”. 
Such a system provides for the transmission of videos in the MPEG-4 format over a multipoint network between a server and a number of users who have heterogeneous bandwidths.
Each user who wishes to receive the video transmits a packet to the server to inform the latter of the maximum bandwidth it can receive.
The various packets from the various users are gathered together in the nodes of the network so as to then transmit to the server just one packet containing the information relating to all the users.
For its part, the server then forms groups of users as a function of the rate constraints specific to the latter and creates, from the video to be transmitted, as many “scalability” levels (hierarchical levels), in terms of time or quality, as there are groups of users formed.
Each scalability level is then transmitted over a multipoint address of the network.
The users then subscribe to a number of scalability levels compatible with their rate constraints and thus each receive a rate that is compatible with their bandwidth constraint.
Taking the techniques proposed in the prior art and briefly described above into account, the Applicant noticed that it would be beneficial to further improve the performance of the existing systems for the transmission of videos over communication networks by further reducing the amount of data transmitted over the network and, where appropriate, by increasing the capacity of the server to meet the clients' wishes as precisely as possible.